DESCRIPTION: (Applicant's Description) In recent years, numerous studies have suggested that the consumption of soybeans and soybean-containing foods may contribute to the lower rates of breast, colon, and prostate cancer in Asia as compared to the U.S. and other Westernized countries. Unfortunately, there is currently no available or tested dietary assessment instrument for the measurement of soyfood consumption and/or isoflavone intake, especially in populations consuming a Western diet. The objective of this proposed study is to develop and validate a soyfood questionnaire that is appropriate for use in epidemiologic studies of diet and health. The specific aims of this proposal are: 1) To conduct a systematic survey of soyfoods available in a large, metropolitan area in the U.S., and use that information to develop a soyfood questionnaire; 2) To validate the soy questionnaire against plasma isoflavone (genistein and daidzein) concentrations; 3) To examine the association between plasma isoflavone concentrations and soy intake as measured by the soyfood questionnaire compared to the Women's Health Initiative Food Frequency Questionnaire (FFQ), which contains only two questions on soyfoods (soy milk and tofu). We propose to develop a soyfood questionnaire and test its validity. Specifically, we will assess the bias and precision of genistein and daidzein intake estimated from a soyfood questionnaire with the plasma levels of these compounds. This study takes advantage of already collected data and requests resources needed to: 1) collect data on additional individuals; 2) conduct a more systematic study of soyfood availability; 3) document our nutrient database; and 4) measure plasma genistein and daidzein concentrations. A total sample of 63 men and 63 women will complete soyfood questionnaires, a FFQ, and provide fasting blood samples. This work fills an important methodologic gap in epidemiologic research by providing investigators with a validated instrument for monitoring soyfood and isoflavone exposure in population-based studies in the United States.